Interpretive Summary: The Mexican fruit fly (Mexfly) is a major pest of oranges and grapefruit in Mexico. The grapefruit crop in south Texas is vulnerable to invasions of this pest because of the proximity to the border. A detection of a Mexfly anywhere in the USA triggers quarantine restrictions. Fruit from an impacted grove cannot be shipped without fumigation. By law the impacted grove is under quarantine for a time equivalent to three generations beginning with the original fly find date with the original fly considered as the parent of the first generation. In practice, the quarantine may be from 4 to 7 months, depending on the time of the year. The duration of a generation is calculated from temperature data recorded by the US Weather Service station nearest to the grove. The temperature data is converted to a thermal unit called a “degree-day.” The value is adjusted for the known developmental rate for the Mexfly. In this article, a calendar is provided that allows producers, packers and program managers to predict the expected duration of the quarantine for any week of the year, based on historical weather records.

Technical Abstract:
The Mexican fruit fly is an invasive pest of citrus and other commercial fruits that triggers quarantine restrictions when it is detected in the United States. The citrus crop in south Texas is especially vulnerable to infestations because of its proximity to the border areas of Mexico where the pest is endemic. Under existing protocols, an infested grove is placed under quarantine for a time equivalent to three life-cycles, estimated by a degree-day model to be (754 x 3 =) 2262 degree-days. Depending on the time of year when a grove becomes infested, the quarantine may last from 4-7 months. Under quarantine restrictions, fruit cannot be shipped without fumigation. In practice, the accumulation of degree-days is tracked from local USWS data. Herein a calendar is provided that projects the expected duration of a quarantine for a fly detection for any week of the year, based on historical weather records. Producers, packers, and program managers can use the projection to plan treatment options.